The present disclosure relates to fuel system valves, and particularly to a flow control valve for regulating the discharge of fuel vapor from a fuel tank. This disclosure also relates to such valves which are tank-mounted for venting fuel vapor from various regions inside a vehicle fuel tank to a vapor-recovery canister or other destination. The disclosure also relates to a tank valve which prevents liquid fuel within a tank venting system from entering and contaminating a vapor-recovery canister within the system.
Is it well understood that significant quantities of fuel vapor can escape from a fuel tank through the filler neck to the atmosphere during the refueling of motor vehicles. Early attempts to control the vapor escape focused upon control devices fitted to a fuel-dispensing pump nozzle connected to a service station fuel pump. Later, control devices mounted directly on-board the vehicle were developed. See, for example, U.S. Pat. No. 4,816,045 to Szlaga et al., relating to a vapor-recovery system mounted on the fuel tank filler neck. Tank venting systems which mount to a fuel tank have also been developed as shown, for example, in U.S. Pat. No. 5,156,178 to Harris.
In additional to controlling vapor escape, well-designed tank venting systems also assist in controlling the amount of liquid fuel which can be pumped into the fuel tank during refueling. For safety reasons, fuel systems are designed so that the fuel tank is never completely filled with liquid fuel. Rather, at least a predetermined portion of the space inside the fuel tank is left for liquid fuel and fuel vapor expansion. Although fuel pump nozzles typically include sensors for shutting off the flow of liquid fuel into the fuel tank when the fuel tank is nearly filled, fuel pump users may manually override the sensors by continuing to pump fuel after the sensors have automatically and temporarily shut the pump nozzle off. To assist in preventing tank overfill under such conditions, a tank venting system is usually provided with a xe2x80x9cfill-limitxe2x80x9d control system which assists in triggering the nozzle shut-off mechanism when the level of liquid fuel in the fuel tank has risen to a predetermined level. See, for example, the fill-limit control system disclosed in U.S. Pat. No. 4,816,045 to Szlaga et al.
Also, it has been recognized that fuel vapor is generated in the fuel tank during operation of the vehicle, for example, by evaporation or by sloshing of the liquid fuel against the walls of the tank. Pressure can build up in the fuel tank as a result of the newly formed fuel vapor unless control devices are provided to vent the fuel vapor from the fuel tank during vehicle operation. Such valves have been referred to as xe2x80x9crun-lossxe2x80x9d valves, vent valves and tank venting rollover valves because they handle the fuel vapor loss during vehicle run and are capable of preventing liquid fuel carryover during vehicle rollover.
Vehicle fuel systems are known to include pressure-relief valves mountable on either fuel tanks or filler necks. In general, the venting portion of these conventional valve assemblies has included a pressure-relief valve positioned in a vent passageway having a surface exposed to the pressure in the tank and a yieldable control spring urging the pressure-relief valve normally to close the vent passageway. In response to a predetermined superatmospheric pressure, the pressure-relief valve is urged in opposition to the control spring to open the vent passageway.
Examples of valves and systems as discussed above include U.S. Pat. Nos. 5,687,778 to Harris; 5,666,989 to Roetker; 4,760,858 to Szlaga and 4,742,844 to Szlaga.
A problem arises with prior devices when the dimension between a full tank fuel level and the inside surface of the tank must be minimized. Prior devices do not provide for venting below the float thereby increasing the distance between the full tank fuel level and the top inside surface of the tank. This situation is exacerbated when the venting valve must be mounted inside the tank. Another problem arises with the prior art when the valves are required to reopen against tank pressure. Such pressure tends to hold the valve in a closed position preventing desirable venting.
Another problem that arises with prior vent designs is that some liquid fuel may flow through the vapor path. In other words, while a passage is provided for venting of the fuel vapor, a portion of liquid may be entrained with the vapor and flow through the vapor path or liquid fuel may splash or slosh into the vapor path.
Disclosed is a vent valve for mounting inside a tank. The valve also facilitates mounting inside the tank to minimize the dimension between a full tank level and a top inside surface of the tank when the valve closes. This is a xe2x80x9cshort shut-offxe2x80x9d condition. Internal venting is provided below the float, through bottom exits, allowing smaller dimensions between the full tank fuel level and top inside surface of the tank.
The disclosure provides a vent valve which also allows the valve to reopen against tank pressures which might otherwise tend to hold the valve shut. This is achieved by employing primary and secondary sealing structures and employing, at least in part, a float weight which least initiates displacement of the primary seal relative to a sealing surface. The disclosure also prevents liquid flow through the vapor path. In the various embodiments disclosed herein a flow channel is provided in the vent valve to create a tortuous path for vapor and liquid to flow. Generally, liquid is removed from the vapor flow and liquid is prevented from splashing or sloshing into the vapor path.